We’ve done some visual illusions here in the past. Now I’d like to offer you an auditory illusion. It’s call the Shepard Tone, and is a carefully constructed sequence of notes that makes you think you’re hearing a sound that is endlessly ascending or endlessly descending. It’s actually transitioning back to an original tone every octave. When it’s skillfully cooked up, it’s really difficult to hear the transition. Here’s the Wiki entry, which leads to some samples.

The trigger for this post is that a software developer that hangs out at KVR has posted four plug-ins that help you construct these types of tones.

They have some examples on their web page of Shepard/Risset tones. I highly recommend that you listen to Vurt’s “52” in the player on the web page. It’s the best-executed example of this illusion that I’ve heard so far. Vurt is a legend at KVR for many reasons, among them that he makes weirder sounds than any other sapient being on the planet. This is Vurtness at its best. Though not its strangest.